2005 NAV system is terrible

When we purchased our sienna we made sure to get the updated map disk. When we go on trips, the NAV system seems to use the close your eyes, throw a dart and select the street to drive on method of routing. Recently we went on a trip that was all interstates, and the NAV system took us on back roads the entire way. I tried to select the main roads, but it would take us to the back roads again. If we had followed the NAV directions the 3 hour trip would have taken 7 or more. I feel that I must be missing something. Are there some settings I can change to make the NAV system useful for more than a map book?